$$ \sum_{i=k}^n (2i-1) $$ I was given the problem shown above. What I did was separate them into two summations as following so it'd be:
$$ 2 \sum_{i=k}^n i - \sum_{i=k}^n 1 $$
I know the second summation will be (n-k+1), but for the first summation, since the bounds aren't a numerical answer, I wasn't sure what it would be since a rule that I know is $$ \sum_{k=1}^n k = \frac{n(n+1)}{2} $$
but k starts at 1. Thank you for the help!